Separation of olefins is an important process in the chemical and petrochemical industry. Currently, the separation is usually done by cryogenic distillation. However, this technology is energy and capital intensive considering the large volume of olefins produced every year. As a result, alternative technologies have been actively sought.
Separation techniques that employ separating agents are attractive alternatives. Reversible olefin complexation in solution using metal ions such as Cu.sup.+ and Ag.sup.+ has been reported. However, these reactions are sensitive to common contaminants such as acetylene, carbon monoxide, and hydrogen sulfide, and the separation schemes use either temperature- or pressure-swing to release olefin.
Some literature reports describe removal and concentration of certain materials, e.g., contaminants, using electrochemically modulated schemes. Separation of ethylene using electrochemical schemes based on simple metal ions in aqueous solution has been reported. For example, a Cu(I)/Cu(II) chloride system has been reported (AICHE J. 1997, 43, 1709-1716) that can reversibly bind ethylene when modulated electrochemically. However, the binding affinity of Cu(I) to ethylene was small due to competitive complexation with chloride anion. In a subsequent report (Inorg. Chem., 1997, 36, 136-140), copper (I) trifluoromethanesulfonate (CuOTf) was used, where the weakly coordinating anion OTf.sup.- allows Cu(I) solution to more efficiently absorb ethylene. Process analyses for certain separation schemes based on electrochemically modulated complexation have appeared in the literature (Chem. Eng. Sci., 1991, 46, 1017-1026; Chem. Eng. Sci., 1992, 47, 1469-1479). The analyses indicate that an electrochemically modulated complexation process can have advantages over normal solvent extractions, as long as suitable complexing agents can be developed. However, an electrochemically driven scheme for olefin separation using transition metal complexes, especially transition metal dithiolene complexes, has not been reported.
An electrochemically driven process has advantages such as possible reduction in volume of the unit and better control of olefin binding and release rates. Moreover, the location and partial pressure of the olefin released can be controlled by specifying the position and electric potential of the electrodes.
Thus, it is highly desirable to develop improved reversible binding agents for use in processes for separating olefins from complex mixtures containing them.
None of the references regarding transition metal dithiolene complexes teaches or suggests that the dithiolene complexes can react with simple olefins (e.g., C.sub.2 to C.sub.6 olefins) reversibly under ambient conditions; or that such a process reversible binding of olefins can be controlled electrochemically. What is desired is an electrochemical process by which simple olefins reversibly bind to a compound or complexing agent using a transition metal dithiolene is selective to such simple olefins in multicomponent olefin streams and, desirably is also tolerant to contaminants and poisons typically present in olefin-containing streams.
Additionally, it would be desirable to have a process for recovering olefins, particularly simple olefins (e.g., C.sub.2 -C.sub.6) from streams containing these simple olefins, as well as other hydrocarbons and contaminants in which the complexing agent reversibly binds the olefin to be recovered.